Self-Aligned Barrier and Capping Layers For Interconnects

ABSTRACT

An interconnect structure for integrated circuits for copper wires in integrated circuits and methods for making the same are provided. Mn, Cr, or V containing layer forms a barrier against copper diffusing out of the wires, thereby protecting the insulator from premature breakdown, and protecting transistors from degradation by copper. The Mn, Cr, or V containing layer also promotes strong adhesion between copper and insulators, thus preserving the mechanical integrity of the devices during manufacture and use, as well as protecting against failure by electromigration of the copper during use of the devices and protecting the copper from corrosion by oxygen or water from its surroundings. In forming such integrated circuits, certain embodiments of the invention provide methods to selectively deposit Mn, Cr, V, or Co on the copper surfaces while reducing or even preventing deposition of Mn, Cr, V, or Co on insulator surfaces. Catalytic deposition of copper using a Mn, Cr, or V containing precursor and an iodine or bromine containing precursor is also provided.

RELATED APPLICATIONS

This patent disclosure is a divisional application of U.S. patentapplication Ser. No. 13/962,856, filed Aug. 8, 2013, which is adivisional application of U.S. patent application Ser. No. 12/908,323,filed Oct. 20, 2010, now U.S. Pat. No. 8,569,165, which claims thebenefit of the earlier filing date of U.S. Patent Application No.61/254,601, filed on Oct. 23, 2009, and U.S. Patent Application No.61/385,868, filed on Sep. 23, 2010, the contents of which are herebyincorporated by reference herein in their entireties.

This patent disclosure is related to U.S. patent application Ser. No.12/408,473, filed on Mar. 20, 2009, which claims the benefit of thefiling date of U.S. Patent Application No. 61/038,657, filed on Mar. 21,2008, U.S. Patent Application No. 61/043,236, filed on Apr. 8, 2008, andU.S. Patent Application No. 61/074,467, filed on Jun. 20, 2008, thecontents of which are hereby incorporated by reference herein in theirentireties.

COPYRIGHT NOTICE

This patent disclosure may contain material that is subject to copyrightprotection. The copyright owner has no objection to the facsimilereproduction by anyone of the patent document or the patent disclosureas it appears in the U.S. Patent and Trademark Office patent file orrecords, but otherwise reserves any and all copyright rights.

INCORPORATION BY REFERENCE

All patents, patent applications and publications cited herein arehereby incorporated by reference in their entirety in order to morefully describe the state of the art as known to those skilled therein asof the date of the invention described herein.

BACKGROUND

Copper (Cu) is replacing aluminum as the material of choice for wiringof microelectronic devices, such as microprocessors and memories.However, the presence of copper in semiconductors such as silicon causesdefects that can prevent the proper functioning of transistors formed inthe semiconductor. Copper also increases the leakage of current throughinsulators, such as silicon dioxide, placed between the copper wires.Therefore use of copper wiring demands that efficient diffusion barrierssurround the copper wires, to keep the copper confined to its properlocations.

While many efforts at providing diffusion barrier layers around copperhave been attempted, they all suffer from some form of disadvantage.Disadvantages include unacceptably high dielectric constant (such as SiCor Si₃N₄) leading to increased capacitances lowering the speed withwhich signals can be transmitted through the copper wiring, difficultiesin processing (such as electroless deposition of CoWP or CoWB) leadingto electrical shorts over insulators between copper wires, increasedresistance of copper through incorporation of other materials (such asCoWP, CoWB, or Mn) used to form the barrier layers, increased resistanceof copper through restriction of the copper grain growth during annealcaused by presence of impurities (such as Mn), poor adhesion of thebarrier layer (such as MnO_(x)) to copper, and the like.

Other efforts have focused on growth of the copper layer, such as growthof copper in narrow trenches and holes (also called vias) on top ofbarrier layers. To this effect, iodine has been proposed as a suitablecatalyst in growing copper using a CVD technique. However, becauseiodine does not readily adhere to the barrier layers (such as TaN andTiN), a thin copper seeding layer or activation of the barrier layerwith plasma pretreatment is needed within the trenches and holes, whichhas been extremely difficult to perform.

SUMMARY

This technology relates to copper interconnections used inmicroelectronics, and more particularly relates to materials andtechniques to secure robust adhesion between the copper and thesurrounding materials, providing barriers to prevent diffusion of copperout of the wiring, keeping oxygen and water from diffusing into thecopper, and keeping the copper wires from being damaged by the electriccurrent that they carry.

A process is described for forming a self-aligned diffusion barrier inmicroelectronic devices without the disadvantage of having a metallicimpurity present in the Cu during or after the anneal. In one embodimenta metal such as Mn, Co, Cr or V is reacted with the surfaces of theinsulator prior to deposition of a Cu-containing seed layer. In certainembodiments, the Mn, Co, Cr or V is delivered to the surfaces by aconformal chemical vapor deposition (CVD) process that does not involvethe use of any oxygen-containing co-reactant along with the precursorfor Mn, Co, Cr or V.

In certain embodiments, the CVD process may further comprise the use ofa nitrogen-containing co-reactant, such as ammonia, therebyincorporating an electrically conductive metal nitride on or near thesurfaces exposed to the vapors. The presence of metal nitride, such asmanganese nitride, has been found to increase the adhesion tosubsequently-deposited copper layers.

According to certain embodiments of the invention, this process does notincrease via resistance by formation of barriers at the bottoms of thevias. Following the metal and/or metal-nitride-producing reaction, a Cuseed layer is deposited, preferably by CVD. The seed layer can also bedeposited as a copper compound, such as copper oxide (Cu₂O), coppernitride (Cu₃N) or copper oxynitride (CuO_(z)N_(w)), which is laterreduced to Cu.

In another aspect of the invention, Mn, Co, Cr or V is deposited on theplanar surface of a partially completed interconnect just after a CMPstep (i.e., a planarized structure). On the top of the insulatingportions of the surface, the Mn, Co, Cr or V reacts with silicon andoxygen contained in the insulator to form an insulating metal silicatelayer, e.g., a MnSi_(x)O_(y) layer where the metal is Mn. In the regionwhere the metal Mn is deposited on the tops of the Cu lines (the tops ofthe trenches filled with Cu), the Mn dissolves into the top layers ofthe Cu to form a Cu—Mn alloy. Then a blanket deposition of the insulatorfor the next higher level of insulator is formed over both the Cu—Mn andMnSi_(x)O_(y) regions. During the deposition and/or during lateranneals, the Mn in the Cu—Mn surface layer diffuses upward to react withthe insulator to form a MnSi_(x)N_(y) diffusion barrier between the Cuand the insulator, in the embodiment in which the initially-depositedpart of this insulator is Si₃N₄. The presence of this MnSi_(x)N_(y)layer also increases the adhesion between the Cu and the insulator aboveit.

Strongly adherent diffusion barrier and adhesion layers that surroundthe Cu on all of its surfaces can be obtained. The MnSi_(x)O_(y) andMnSi_(x)N_(y) layers provide highly conductive, strongly adherent anddurable copper layers for, e.g., the production of electronic elements,circuits, devices, and systems.

In another aspect of the invention, Mn, Co, Cr or V is depositedselectively only on the metallic areas of the planar surface of apartially completed interconnect just after a CMP step (i.e., aplanarized structure). At the same time little or no Mn, Co, Cr or V isdeposited on nearby surfaces of insulators. The process increases theadhesion of copper to subsequently-deposited insulators whilemaintaining very low electrical leakage across insulators betweenneighboring copper conductors. This process increases the lifetime ofcopper interconnects before they fail due to electromigration.

In certain embodiments, the present application describes a process forforming an integrated circuit interconnect structure. The processcomprises: providing a partially-completed interconnect structure thatincludes an electrically insulating region and an electricallyconductive copper-containing region, the partially-completedinterconnect structure having a substantially planar surface; depositinga metal (M) selected from the group consisting of manganese, chromiumand vanadium on or into at least a portion of the electricallyconductive copper-containing regions; depositing an insulating film onat least a part of the deposited metal, wherein the region of thedeposited insulating film in contact with said at least a part of thedeposited metal is substantially free of oxygen; and reacting at least apart of the deposited metal with the insulating film to form a barrierlayer, wherein the electrically conductive copper-containing region issubstantially free of elemental metal (M).

In other embodiments, the process includes: providing apartially-completed interconnect structure having a via or a trench, thevia or trench including sidewalls defined by one or more electricallyinsulating materials and an electrically conductive copper-containingbottom region; depositing a metal (M) selected from the group consistingof manganese, chromium and vanadium on the partially-completedinterconnect structure; forming second insulating sidewall regionsthrough reaction of the deposited metal and said one or moreelectrically insulating materials; removing or diffusing away the metalfrom the bottom region to expose the electrically conductivecopper-containing bottom region; and filling the via or trench withcopper.

In other embodiments, the manganese may be replaced by chromium orvanadium.

In certain embodiments, a process is provided for the bottom-up fillingof trenches or holes with copper or copper manganese alloy by a CVDmethod using manganese nitride as a underlayer and iodine as asurfactant catalyst. The copper or copper manganese alloy is depositedwith a CVD method using appropriate vapor sources. Conformal depositionin sub-100 nm trenches can be achieved. Conformally deposited manganesenitride films show barrier properties against Cu diffusion and enhanceadhesion between Cu and dielectric insulators. Release of adsorbediodine atoms from the surface of manganese nitride films allows iodineto act as a surfactant catalyst floating on the surface of a growingcopper layer. As the copper layer grows, iodine is continually releasedfrom the deposition interface to ‘float’ to the top of the growingcopper layer and to serve as a surface catalyst for the next layer ofcopper to be deposited. As a result, void-free bottom-up filling of CVDof pure copper or copper-manganese alloy has been achieved in trenchesnarrower than 20 nm with aspect ratios over 9:1. Upon post-annealing,manganese in the alloy diffuses out from copper through the grainboundaries and forms a self-aligned layer to further improve adhesionand barrier properties at the copper/insulator interface. This processprovides nanoscale interconnects for microelectronic devices with higherspeeds and longer lifetimes.

Materials and techniques are provided to secure robust adhesion betweenthe copper and the surrounding materials, to form barriers to preventdiffusion of copper out of the wiring, to prevent oxygen and water fromcorroding the copper, and to keep the copper wires from being damaged bythe electric current that they carry.

In one embodiment, a partially completed interconnect structure havingopen trenches (that will contain wires) and holes (vias that willconnect one level of wires with wires already formed) can be subjectedto one or more CVD processes. CVD can be used to deposit manganese onthe walls of the trenches and vias, as well as on exposed portions ofany conductors already formed at the bottoms of the vias. Next, CVD canbe used to chemisorb iodine onto the manganese-coated surfaces. Finally,CVD of copper can be carried out in such a way that iodine catalyzes thebottom-up filling of vias and trenches without any seams or voids.

In another embodiment, the a layer of manganese nitride (MnN_(x), 0<x<1)can be formed, followed by chemisorption of iodine on the manganesenitride, and followed by catalytically-enhanced CVD of void-free copperto fill the vias and trenches.

In other embodiments, a layer of manganese nitride (MnN_(x), 0<x<1) canbe formed, followed by chemisorption of iodine and followed bycatalytically-enhanced CVD of a thin layer of copper. Additional iodinecan then be further chemisorbed onto the surface of this thin copperlayer, followed by additional CVD of copper that may be even moreefficiently catalyzed by the larger amount of iodine resulting from bothchemisorption steps.

In still other embodiments, alternating steps of CVD manganese and CVDcopper, resulting in filling of the trenches and vias with acopper-manganese nanolaminate can further be carried out. Heating thisstructure can permit diffusion of the manganese to nearby insulatorsurfaces, where it can increase the adhesion strength of the copper tothe insulators and form a self-aligned barrier to diffusion of copper,water and oxygen. After the out-diffusion of manganese, the interconnectcan become pure, highly conductive copper bonded strongly to theinsulator surfaces by the manganese.

In other embodiments, after the initial manganese and iodinedepositions, copper and manganese precursor vapors can simultaneously beintroduced into the deposition zone of a CVD reactor, along with anynecessary reducing agents, such as hydrogen, to deposit a void-freecopper-manganese alloy.

In alternate embodiments, CVD can be used to form a thin layercomprising Mn, I and Cu, which can serve as a seed layer forelectroplating Cu.

Precursors suitable for CVD of manganese include manganese amidinates,such as manganese(II) bis(N,N′-dialklyamidinates), which can be reducedwith hydrogen to give manganese metal, or reacted with ammonia todeposit manganese nitride at low temperatures and with dense nucleationon insulator surfaces.

Many precursors are known for CVD of copper metal. Copper amidinates,such as copper(I) N,N′-dialkylamidinate dimers, are particularlysuitable because their high thermal stability and high reactivity permitpure copper to be deposited by hydrogen reduction at low temperatureswith dense nucleation on iodine-covered manganese or manganese nitridesurfaces.

Other features and advantages of the invention will be apparent from thefollowing description and accompanying figures, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross section of the top of a partially completedinterconnect wiring structure in accordance with the invention, after aChemical Mechanical Polishing (CMP) step.

FIG. 2 is the structure of FIG. 1 after a metal deposition.

FIG. 3 is the structure of FIG. 2 after removal of metal silicate.

FIG. 4 is the structure of FIG. 3 after a blanket insulator isdeposited.

FIG. 5 is the structure of FIG. 4 after lithography and etching of viasand trenches in the insulator.

FIG. 6 is the structure of FIG. 5 after an anneal.

FIG. 7 is the structure of FIG. 6 after another metal deposition.

FIG. 8 is the structure of FIG. 7 after an anneal.

FIG. 9 is the structure of FIG. 8 after seed layer deposition andfilling with copper.

FIG. 10 is the structure of FIG. 9 after Chemical Mechanical Polishing.

FIG. 11 is a cross-sectional high-resolution transmission micrograph ofthe result of CVD Mn on a Cu/SiO₂/Si substrate.

FIG. 12 is a scanning electron micrograph of (a) Cu/SiO₂/Si and (b)Cu/MnSi_(x)O_(y)/Si after annealing at 500° C. and etching off the Cu,along with elemental analyses of the surfaces.

FIG. 13 shows capacitance-voltage curves for samples of (a) Cu/SiO₂/Siand (b) Cu/MnSi_(x)O_(y)/SiO₂/Si before and after annealing at 400° C.

FIG. 14 shows capacitance-voltage curves for samples of (a) Cu/SiO₂/Siand (b) Cu/MnSi_(x)O_(y)/SiO₂/Si before and after annealing at 250° C.under a 1 MV/cm electric field.

FIG. 15 shows a cross-section of a MnSi_(x)O_(y) layer formed by CVD ona low-k insulator.

FIG. 16 shows the Rutherford Backscattering spectra (RBS) of a coppersurface and a SiO₂ surface, each of which was exposed to the same CVDconditions, which deposited 8 nm of manganese only on the copper, whiledepositing no manganese on the SiO₂.

FIG. 17 shows the distribution of manganese near the surface of a copperlayer that had been exposed to CVD of manganese.

FIG. 18 shows a plot of the adhesion energy of a copper-manganese alloyto silicon-containing insulators as a function of the manganese tosilicon ratio at the interface.

FIG. 19 shows X-ray Photoelectron Spectra of insulator surfaces subjectto CVD manganese with the inventive process along with less selectiveprocesses.

FIG. 20 is a scanning electron micrograph (SEM) of narrow holes linedwith MnN_(x) in accordance with certain embodiments;

FIG. 21 is a transmission electron micrograph (TEM) of narrow trencheslined with MnN_(x) and filled with Cu in accordance with certainembodiments;

FIG. 22 shows X-ray photoelectron spectra (XPS) showing that iodineremains on the surface of the copper throughout the deposition ofcopper.

FIG. 23 is a scanning electron micrograph of narrow trenches lined withMnN_(x) and filled with Cu in accordance with certain embodiments;

FIG. 24 shows a trench partly filled by iodine-catalyzed CVD of copperon an MnN_(x) lined trench.

FIG. 25 shows SEM and energy-dispersive X-ray analysis (EDX) datashowing that MnN_(x) is a barrier to diffusion of copper;

FIG. 26 is a SEM of narrow trenches lined with MnN_(x) and filled with aCu—Mn nanolaminate in accordance with certain embodiments;

FIG. 27 shows that iodine remains on the surface during deposition of acopper-manganese nanolaminate.

FIG. 28 is a SEM of narrow trenches lined with MnN_(x) and filled with aCu—Mn alloy in accordance with certain embodiments;

FIG. 29 shows that iodine remains on the surface during deposition of acopper-manganese alloy.

FIG. 30 is an SEM of polyimide plastic coated with MnN_(x) and Cu inaccordance with certain embodiments; and

FIG. 31 is an SEM of plastic circuit board material coated with MnN_(x)and Cu in accordance with certain embodiments.

DETAILED DESCRIPTION OF THE INVENTION

A partially completed multi-level wiring structure for a microelectronicdevice is shown in FIG. 1. This structure comprises a substantiallyplanar surface comprising insulating areas 10, e.g., silica, andelectrically conducting areas 20, e.g., copper, forming the top of acompleted lower level of wiring, separated by a diffusion barrier 25. Insome embodiments, this diffusion barrier can comprise manganesesilicate. Typically, the device at this stage has been processed by CMPfollowed by cleaning. It should be noted that although the discussionexemplifies the invention using Mn, other metal precursors that contain,for example, Co, Cr, or V, can just as easily be carried used.

Next, as shown in FIG. 2, Mn (or Co, or Cr, or V) metal is deposited onthe surface. The Mn reacts with the exposed areas of the insulator 10 toform an insulating MnSi_(x)O_(y) layer marked 30 in FIG. 2. In theexposed Cu areas of the surface 20, the Mn diffuses into the upperportion of the Cu to form a CuMn alloy 40. The location of the uppersurface prior to deposition is indicated by arrows 45, 45′. Typically,Mn is deposited on a heated substrate. If the temperature of thesubstrate is high enough (typically over 150° C.) and the deposition ofMn is slow enough, then the reaction and diffusion of the Mn may becomplete by the end of the deposition. If the reaction with theinsulator and the diffusion into the Cu are not complete duringdeposition, then a post-deposition anneal may be used to complete thereaction and diffusion.

Mn may be deposited by any convenient method, including chemical andphysical methods. Chemical methods include chemical vapor deposition(CVD) and atomic layer deposition (ALD). Physical methods includesputtering and evaporation. Because the substrate is planar, stepcoverage by the deposition method is not critical to this step. Thusphysical methods, which have poor step coverage, are adequate for thisdeposition step. CVD can also be used in this step whether or not thespecific CVD process has good step coverage.

The MnSi_(x)O_(y) layer 30 can optionally be removed after Mndeposition, as is shown in FIG. 3. The MnSi_(x)O_(y) layer 30 formed inthe last step is an electrical insulator, but its leakage current may behigher than desired in some applications. In such cases, this metalsilicate layer 30 may be removed, in order to reduce the leakage currentin devices. The silicate layer 30 may be removed by any convenientmeans, such as polishing, wet etching or dry etching. The removal may benon-selective, removing copper at the same rate as the silicate, therebymaintaining a flat surface. Alternatively, the silicate layer 30 may beremoved selectively without removing copper, as is illustrated in FIG.3. The resulting uneven surface requires a conformal method to depositthe blanket insulator in the next step.

Alternatively, rather than depositing Mn (or Co, or Cr, or V) on boththe insulating and conductive surfaces of FIG. 1, the surfaces can bepretreated to selectively deposit manganese on the copper surfaces. Asused herein, “selective deposition” refers to preferential deposition ofa material onto one surface while little or no deposition occurs on adifferent surface. Accordingly, the surface can be pretreated topreferentially deposit manganese on the copper surface and to reduce oreliminate deposition of manganese on the insulator areas).

Reactive sites on the insulator surface can be deactivated usingprotecting agents prior to the CVD of manganese. This deactivation canbe accomplished by reaction of the insulator surface with alkylsilanecompounds either in the vapor phase or in solution. For example,effective deactivating compounds comprise dialkylamide groups bonded tosilicon, such as bis(N,N-dialkylamino)dialkylsilanes andN,N-dialkylaminotrialkylsilanes. Exemplary reagents of these two typesinclude bis(N,N-dimethylamino)dimethylsilane, (CH₃)₂Si(N(CH₃)₂)₂, and(N,N-dimethylamino)trimethylsilane, (CH₃)₃SiN(CH₃)₂.

In certain embodiments, the deactivation can be accomplished by reactionof the insulator surface with two or more alkylsilane compounds eitherin the vapor phase or in solution to synergistically reduce reactivityof the insulating surfaces. As used herein, “synergistic” means that theuse of the two or more protecting agents leads to a greater deactivationeffect as compared to the deactivation effect obtained by use of theindividual protecting agents.

In certain embodiments, complete prevention of manganese or cobaltdeposition on the insulators has been achieved by the sequentialexposure of an insulator surface to a bis(N,N-dialkylamino)dialkylsilaneand then to a N,N-dialkylaminotrialkylsilane. Under the same reactionconditions, it has been discovered that neither of these types ofdeactivating compounds reacts with a clean, oxide-free copper surface.Thus CVD of manganese or cobalt on copper surfaces is not prevented bythese reagents.

Thereafter, a manganese amidinate vapor and hydrogen gas are broughtinto contact with a heated substrate. On parts of the substrate surfacethat are composed of copper 20, a thin, continuous layer ofcopper-manganese alloy 40 is formed near the surface of the copper. Onparts of the substrate surface made of insulators 10, such as SiO₂ orSiCOH, little or no manganese is deposited. In certain embodiments, thetemperature of the heated surface can be in a suitable range, typically200 to 350° C., or more preferably 250 to 300° C.

As noted above, other metals, such as Co, Cr, or V, can be selectivelydeposited over the copper surfaces. For example, cobalt metal can bedeposited on copper surfaces, while little or no cobalt is deposited oninsulator surfaces. In such embodiments, a cobalt amidinate vapor andhydrogen gas are brought into contact with a heated substrate. On partsof the substrate surface that are composed of copper 20, a thin,continuous layer of cobalt 40 is formed on the surface of the copper. Onparts of the substrate surface made of insulators 10, such as SiO₂ orSiCOH, little or no cobalt is deposited. In certain embodiments, thetemperature of the heated surface can be in a suitable range, typically180 to 250° C., or more preferably 200 to 220° C.

A blanket insulator layer 50 is next deposited on the structure shown inFIG. 3 (either with or without planarization), as shown in FIG. 4. Notethat the structure in FIG. 4 does not include the silicate layer 30above insulating layer 10. Any of the methods known in the art may beused to make this insulator layer, including plasma-enhanced CVD or spincoating. Insulator compositions comprising Si and O may be used. Incertain embodiments, insulator compositions comprising Si but which issubstantially free of O, such as SiN, SiC, SiCN, and the like, may beused. In certain embodiments, insulator layers can be built up bydeposition of several sub-layers of insulating material, each adding aspecific functionality to the overall insulating layer. For example, afirst insulating sub-layer 51 which enhances adhesion to themanganese-doped copper layer underneath it, such as a Si₃N₄, may beused. In certain embodiments, sub-layer 51 may be substantially free ofoxygen. In certain embodiments, sub-layer 51 that is substantially freeof oxygen may enhance adhesion to the manganese-doped copper layer overthan that obtained by adhesion of a sub-layer 51 which comprises oxygen.Next an etch-stop sub-layer 52, such as silicon carbide, may bedeposited on top of sub-layer 51. The etch-stop sub-layer 52 can help todefine the proper depth for etching of the holes (vias). In certainembodiments, the next insulating sub-layer 53 may be a porous dielectricwith a very low dielectric constant (typically k less than about 2.5).The final insulating sub-layer 54 may be a denser non-porous dielectricwith a higher dielectric constant (k greater than about 2.5), which canhelp to protect the more fragile porous dielectric layer from mechanicaldamage, as well as keeping water from entering into the pores of theporous dielectric. In certain embodiments, sub-layers 53 and 54 maycontain Si and O. Another function of the sub-layer 53 may be as anetch-stop layer for defining the bottoms of trenches through thesub-layer 54. As would be readily apparent to one of ordinary skill inthe art, numerous variations for the specific insulator layer 50 (suchas thickness, layer combinations, material compositions, etc.) arewithin the scope of the present invention. For simplicity, any referenceto insulating layer 50 in the present application should be understoodto encompass one or more of the sub-layers described herein.

Lithography and etching are used to pattern holes (vias) 100 andtrenches 110 into the insulator layer 50. A schematic cross section ofthe resulting structure is shown in FIG. 5.

This structure is annealed to form a MnSi_(x)N_(y) layer 60 (assumingthe use of Si₃N₄ as sub-layer 51) at the interface between theinsulating silica layer 50 and the CuMn alloy layer 40, as shown in FIG.6. The MnSi_(x)N_(y) layer 60 serves as a barrier against diffusion ofCu out of the layer 20 and also provides strong adhesion between the Cu20 and the insulator 50. The MnSi_(x)N_(y) can also serve to preventdiffusion of oxygen or water from the insulator layer 50 into the Culayer 20. After anneal, most of the Mn from the Mn—Cu alloy layer 40 islocated in the MnSi_(x)N_(y) layer 60; however, some Mn may migrateduring anneal to the upper surface of the layer 20 to form a manganeseoxide layer (not shown). Any manganese oxide remaining on the Cu surfacemay be removed by directional sputtering, or by selective etching by avapor such as formic acid or by a liquid acid solution. This isindicated by the slight recession 65 between the upper surface of Culayer 20 and adjacent MnSi_(x)N_(y) layer 60.

Another layer of Mn is deposited next, preferably by a conformal methodsuch as CVD or ALD. This step forms a layer 80 on the walls of the viasand trenches, which can vary from MnSi_(x)O_(y) near the top andMnSi_(x)N_(y) near the bottom if using silica as sub-layer 54 andsilicon nitride as sub-layer 51. This step can further form a top layerof MnSi_(x)O_(y) 90 on the upper surface of insulator layer 50, as shownin FIG. 7. A CuMn alloy layer 70 forms initially on the exposed coppersurface of layer 20, but then the Mn diffuses to form more of theinsulator surfaces such as layer 60. If the formation of these layers isnot complete by the end of the deposition, an additional anneal andpossibly an acid etch is used to form the structure shown in FIG. 8, inwhich the copper 20 layer is substantially free of Mn impurity.

In certain embodiments, manganese nitride, MnN_(x), may also bedeposited on the exposed surfaces of vias 100 and trenches 110. In someother embodiments, manganese nitride, MnN_(x), may also be deposited onlayers 70, 80 and 90. Surprisingly, the use of manganese nitride wasfound to provide at least five beneficial functions. First, themanganese nitride can increase the strength of adhesion between theinsulating material and subsequently-deposited copper. Second, themanganese nitride can serve as an effective barrier layer againstdiffusion of copper, oxygen, and water. Third, the manganese nitride canenhance capture and release of a surface catalyst, such as iodine orbromine, as discussed in greater detail below. These three benefits ofMnN_(x) are similar to those conferred by manganese metal. As anadditional fourth benefit, manganese nitride deposits more continuouslyand uniformly over a surface than pure manganese metal does, because wediscovered that MnN_(x) is more resistant to agglomeration than Mn is.The manganese nitride is preferably deposited by a conformal method,such as CVD, ALD or ionized physical vapor deposition (IPVD). Fifth, wefound that CVD and ALD of MnN_(x) can be accomplished at lowertemperatures and at a higher rate than deposition of manganese metal. Ifit is desirable to use continuous and non-agglomerated manganese metal,it may be formed conveniently by removing nitrogen from manganesenitride, for example by the use of a hydrogen plasma.

Next, a seed layer of Cu is formed, preferably by a conformal methodsuch as CVD, ALD or IPVD. Then the vias and trenches are filled byelectroplating to form the structure shown in FIG. 9. This pure Cu layer120 is annealed to increase the grain size and reduce the resistance.

In certain alternative embodiments, copper can be catalytically grown invias and trenches, such as vias and trenches having a structure similarto that shown in FIG. 8, vias and trenches having the sidewalls andbottom surface deposited with a manganese containing layer, such asmanganese nitride layer, or vias and trenches having an insulatorsurface, such as silica.

In certain embodiments, the vias and trenches may be exposed to amanganese containing precursor to form a manganese containing layer.After the formation of a manganese containing layer (e.g., through avapor deposition technique such as CVD), iodine or bromine containingprecursor, such as ethyl iodide, methyl iodide, di-iodomethane moleculariodine (I₂), bromoethane, or molecular bromine (Br₂), can be introducedto adsorb or chemisorb onto the manganese containing surfaces.Thereafter, copper can be catalytically grown using a vapor depositiontechnique, such as CVD.

Without wishing to be bound by theory, the iodine or bromine containingprecursor may act as a catalyst for the growth of copper for thefollowing reasons, which one of ordinary skill in the art would not haveexpected. Taking iodine as an example, the bond strength between aniodine atom and a manganese atom is known to be much larger than thebond strength between iodine and copper, at least in the gas phase. (Thedata can be found in the CRC Handbook of Chemistry and Physics:D°₂₉₈=197±21 kJ/mol for Cu—I and D°₂₉₈=282.8±9.6 kJ/mol for Mn—I).Therefore, one of ordinary skill in the art would have expected that asmall amount of iodine catalyst (less than a monolayer) would be heldstrongly by the manganese atoms. While the strong iodine-manganese bondmay be desirable to allow iodine to attach to the Mn surface andinitiate the subsequent growth of copper, the iodine attached to themanganese would not be able to float to the copper surface and thuswould not be able to catalyze the copper deposition reactions on itssurface. Accordingly, in certain embodiments, the presence of othercomponents, such as nitrogen in the manganese film, might be able toweaken the manganese-iodine bonds by a sufficient amount so that theiodine can be released to the copper film. As noted above, the MnN_(x)—Ibonds nevertheless must also be strong enough to catch the iodine fromthe gas phase during the initial chemisorption of the iodine.Discovering the suitable combination of properties that allow initialchemisorption followed by release from the Mn containing surfacerequired extensive efforts and was not readily apparent to theinventors. For example, other materials, such as silicon dioxide andtitanium nitride, fail to chemisorb the iodine while other materials,such as cobalt and nickel, readily chemisorb the iodine but then fail torelease it.

After the iodine or bromine containing precursor has been deposited ontothe manganese containing layer, a copper layer can be formed usingtechniques such as CVD, ALD or IPVD.

In certain embodiments, after the first iodine or bromine containingprecursor has been deposited onto the manganese containing layer,manganese and copper containing precursors can be co-deposited, eitheras mixed precursors or separate precursors to form a copper-manganesealloy.

In some other embodiments, after the first iodine or bromine containingprecursor has been deposited onto the manganese-containing layer,manganese, copper, and iodine/bromine containing precursors can beco-deposited, either as mixed precursors or separate precursors to forma copper-manganese alloy where the additional iodine/bromine can serveto ensure or even further promote the catalytic growth of thecopper-manganese alloy.

In certain embodiments, electroplating of copper can be performed afterdeposition of copper or copper-manganese alloy described above.

After the Cu or Cu—Mn alloy has been deposited and/or electroplated, theCu or Cu—Mn alloy layer 120 can be annealed to increase the grain sizeand reduce the resistance.

Finally the excess copper is removed by CMP to create the structureshown in FIG. 10. This stage corresponds to the structure of FIG. 1,with one more stage of wiring completed.

In one or more embodiments, vapor deposition is used to deposit a metalM selected from the group of Mn, Co, Cr and V. Metal amidinate compoundsof the formula [M(AMD)_(m)]_(n) may be used as precursors, where AMD isan amidinate ligand and typically m=2 or 3 and n=1 or 2. For the casem=2 and n=1, these compounds may have the following structure:

in which R¹, R², R³, R^(1′), R^(2′) and R^(3′) are groups made from oneor more non-metal atoms, such as hydrogen, hydrocarbon groups,substituted hydrocarbon groups, and other groups of non-metallic atoms.In one CVD method for depositing Mn, a manganese amidinate vapor isbrought into contact with a heated substrate. Where the substrate is Cu,a CuMn alloy is formed. Where the substrate contains silicon and oxygen,an insulating surface layer of MnSi_(x)O_(y) is formed. In order forthese layers to be formed, the temperature of the heated surface shouldbe sufficiently high, typically over 150° C., or preferably over 300° C.

In one or more embodiments, the Mn-containing precursor can be amanganese amidinate having the formula, [Mn(AMD)_(m)]_(n), where AMD isan amidinate and m=2 or 3 and n can range from 1 to 3. Some of thesecompounds for m=2, n=1 have a structure 1,

in which R¹, R², R³, R^(1′), R^(2′) and R^(3′) are groups made from oneor more non-metal atoms, such as hydrogen, hydrocarbon groups,substituted hydrocarbon groups, and other groups of non-metallic atoms.In some embodiments, R¹, R², R³, R^(1′), R^(2′) and R^(3′) may be chosenindependently from hydrogen, alkyl, aryl, alkenyl, alkynyl,trialkylsilyl, alkylamide or fluoroalkyl groups or other non-metal atomsor groups.

Exemplary hydrocarbon groups include C₁-C₆ alkyl, C₂-C₆ alkenyl andC₂-C₆ alkynyl groups. They can be branched or unbranched.

“Alkyl group” refers to a saturated hydrocarbon chain that may be astraight chain or branched chain or a cyclic hydrocarbon group,containing the indicated number of carbon atoms. For example, C₁-C₆indicates that the group may have from 1 to 6 (inclusive) carbon atomsin it. Examples of alkyl groups include, but are not limited to, ethyl,propyl, isopropyl, butyl, and tert-butyl groups. Examples of cyclicalkyl groups include, but are not limited to, cyclopropyl,cyclopropylmethyl, cyclobutyl, cyclopentyl, cyclohexyl,cyclohexylmethyl, cyclohexylethyl, and cycloheptyl groups.

“C₂-C₆ alkenyl group” refers to a straight or branched chain unsaturatedhydrocarbon containing 2-6 carbon atoms and at least one double bond.Examples of a C₂-C₆ alkenyl group include, but are not limited to,groups derived by removing a hydrogen from ethylene, propylene,1-butylene, 2-butylene, isobutylene, sec-butylene, 1-pentene, 2-pentene,isopentene, 1-hexene, 2-hexene, 3-hexene, and isohexene.

“C₂-C₆ alkynyl group” refers to a straight or branched chain unsaturatedhydrocarbon group containing 2-6 carbon atoms and at least one triplebond. Examples of a C₂-C₆ alkynyl group include, but are not limited to,groups derived by removing a hydrogen from acetylene, propyne, 1-butyne,2-butyne, isobutyne, sec-butyne, 1-pentyne, 2-pentyne, isopentyne,1-hexyne, 2-hexyne, and 3-hexyne.

“Substituted hydrocarbon group” refers to a saturated or unsaturated,straight or branched chain hydrocarbon containing 1-6 carbon atoms thatcan be further substituted with other functional groups, such as halogenor boron, or boron-containing groups.

“Halogen” refers to an atom of fluorine, chlorine, bromine, or iodine.Halogenated hydrocarbons include fluorinated, chlorinated or brominatedalkyl. Exemplary fluorinated hydrocarbons include fluoroalkyl,fluoroalkenyl and fluoroalkynyl groups and combinations thereof.

“Groups of non-metallic atoms” include nitrogen-containing andsilicon-containing groups. Exemplary nitrogen-containing R groupsinclude amines (NR′R″), in which R′ and R″ include one or more of H,C₁-C₆ alkyl, C₂-C₆ alkenyl or C₂-C₆ alkynyl group and combinationsthereof.

Exemplary silicon-containing R groups include silyl groups (SiR′R″R′″),in which R′, R″ and R′″ include one or more of H, C₁-C₆ alkyl, C₂-C₆alkenyl or C₂-C₆ alkynyl group and combinations thereof.

In some embodiments, R¹, R², R³, R^(1′), R^(2′) and R^(3′) are eachindependently alkyl or fluoroalkyl or silylalkyl groups or alkylamidegroups. In some embodiments, the R^(n) groups contain 1 to 4 carbonatoms. In other embodiments, the Mn precursor is an oligomer ofstructure 1, with n=2 or more. The manganese amidinate may comprisemanganese(II) bis(N,N′-diisopropylpentylamidinate), corresponding totaking R¹, R², R^(1′) and R^(2′) as isopropyl groups, and R³ and R^(3′)as n-butyl groups in the general formula 1.

In a CVD method, bis(N,N′-diisopropylpentylamidinato)manganese(II) vaporis flowed over a surface that has been heated to a temperatures of 100to 500° C., or more preferably 150 to 400° C. A CuMn alloy is formed onthe exposed copper surfaces. A MnSi_(x)O_(y) layer is formed as adiffusion barrier over the insulating areas. In some embodiments, themanganese content of the MnSi_(x)O_(y) layer and the CuMn layer isequivalent to a manganese metal film with thickness of 1 to 10 nm, ormore preferably a thickness of 2 to 5 nm. Alternatively, the vapor ismixed with dihydrogen gas (H₂) at a temperature above 90° C. and usedfor the CVD process.

Manganese amidinates may be made by any conventional method. See, e.g.,WO 2004/046417, which is incorporated by reference in its entirety.

In one or more embodiments, the metal precursor may includecyclopentadienyl and carbonyl ligands, corresponding to the generalformula (Cp)_(q)M_(r)(CO)_(s) where Cp is an cyclopentadienyl radicalsubstituted by up to five groups, and q, r, and s can be any positiveinteger. These compounds may have the following structure:

In one or more embodiments, the Mn-containing precursor can be amanganese cyclopentadienyl tricarbonyl having the formula, (Cp)Mn(CO)₃.Some of these compounds have a structure 2,

in which the R¹, R², R³, R⁴, and R⁵ groups are made from one or morenon-metal atoms, such as hydrogen, hydrocarbon groups, substitutedhydrocarbon groups, and other groups of non-metallic atoms, as describedherein above. In some embodiments, R¹, R², R³, R⁴, and R⁵, may be chosenindependently from hydrogen, alkyl, aryl, alkenyl, alkynyl,trialkylsilyl or fluoroalkyl groups or other non-metal atoms or groups.In some embodiments, R¹, R², R³, R⁴ and R⁵ are each independently alkylor fluoroalkyl or silylalkyl groups or alkylamide groups. In someembodiments, the R^(n) groups contain 1 to 4 carbon atoms. A preferredcompound of this type is commercially availablemethylcyclopentadienylmanganese tricarbonyl, (MeCp)Mn(CO)₃, in which R¹is a methyl group and the other R^(n)'s are hydrogen.

In one or more embodiments, the metal precursor may include two Cpligands, with formula M(Cp)₂ where Cp is a cyclopentadienyl radicalsubstituted by up to five groups. These compounds may have the followingstructure:

In one or more embodiments, the Mn-containing precursor can be amanganese cyclopentadienyl having the formula, Mn(Cp)₂. Some of thesecompounds have the formula 3,

in which R¹, R², R³, R⁴, R⁵, R^(1′), R^(2′), R^(3′), R^(4′) and R^(5′)are groups made from one or more non-metal atoms, such as hydrogen,hydrocarbon groups, substituted hydrocarbon groups, and other groups ofnon-metallic atoms, as described herein above. In some embodiments, R¹,R², R³, R⁴, R⁵, R^(1′), R^(2′), R^(3′), R^(4′) and R^(5′) may be chosenindependently from hydrogen, alkyl, aryl, alkenyl, alkynyl,trialkylsilyl or fluoroalkyl groups or other non-metal atoms or groups.In some embodiments, R¹, R², R³, R⁴, R⁵, R^(1′), R^(2′), R^(3′), R^(4′)and R^(5′) are each independently alkyl or fluoroalkyl or silylalkylgroups or alkylamide groups. In some embodiments, the R^(n) groupscontain 1 to 4 carbon atoms.

In certain embodiments, the manganese precursorbis(N,N′-diisopropylpentylamidinato)manganese(II) may be prepared asdescribed in US Patent Application US 2009/0263965, the contents ofwhich is incorporated by reference in its entirety, or obtained from theDow Chemical Company. Its chemical formula is shown below:

Iodine precursors, such as ethyl iodide or elemental I₂ are commerciallyavailable from many commercial sources.

A Cu layer (a seed layer or a full layer) may be deposited conformallyby methods such as CVD or ALD. ALD methods are described, for example,by Zhengwen Li, Antti Rahtu and Roy G. Gordon in the Journal of theElectrochemical Society, volume 153, pages C787-C794 (2006) and byZhengwen Li and Roy G. Gordon in the journal Chemical Vapor Deposition,volume 12, pages 435-441 (2006). CVD methods are described in the paperby Hoon Kim, Harish B. Bhandari, Sheng Xu and Roy G. Gordon, which waspublished in the Journal of the Electrochemical Society, volume 155,issue 7, pages H496-HSO3 (2008). In this reference, smooth thin layersof copper oxynitride or copper oxide are first deposited usingconventional vapor deposition techniques and then the deposited layersare reduced to smooth copper films by reduction with a hydrogen plasmaat room temperature. Another method for reducing copper oxide films tocopper metal is by reaction with liquid solutions of reducing agentssuch as dimethylamineborane or metal borohydrides.

In certain embodiments, the copper precursor copperN,N′-di-sec-butylacetamidinate may be utilized, which can be prepared asdescribed in Inorganic Chemistry, volume 44, pages 1728-1735 (2005), thecontents of which is incorporated by reference in its entirety, orobtained from the Dow Chemical Company. Its chemical formula is shownbelow:

Other copper compounds can also be used for the iodine-catalyzed CVD ofcopper, including copper beta-diketonates, copper beta-ketoiminates,copper diketiminates, copper cyclopentadienyls, copper alkoxides andcopper aminoalkoxides. Specific examples of these general classesinclude 1,1,1,5,5,5-hexafluoro-2,4-pentadionato copper(I)vinyltrimethylsilane (sometimes known as (hfac)CuVTMS),1,1,1,5,5,5-hexafluoro-2,4-pentadionato copper(I)(3,3-dimethyl-1-butene) (sometimes known as (hfac)CuDMB),bis(1,1,1,5,5,5-hexafluoro-2,4-pentadionato) copper(II) (sometimes knownas Cu(hfac)₂),(N(1(dimethylvinylsiloxy)-1-methylethano)-2-imino-4-pentanoato)copper(I)(a copper ketominate),(N(2(vinyldimethylsiloxy)propyl)-2-imino-4-pentenoato) copper(I),bis[[2-(4,5-dihydro-3H-pyrrol-yl)-1-methyl-vinyl]ethyl-aminate]copper(II)(a copper diketiminate) and methylcyclopentadienyl copper(I) ethylene.Another suitable copper precursor is the copper(I) beta-diketiminatewhose formula is shown below:

As noted above, electrochemical deposition can be used to fill thetrenches and vias with copper by techniques known in the art.Electrochemical deposition may be able to provide pure copper withoutvoids or seams in a cost-effective process.

In the foregoing description, the present invention has been describedmainly with respect to Mn metal. However, the present inventionencompasses other metals, such as cobalt, vanadium and chromium metalsas well. Accordingly, these metals can be interchanged with manganesefor the descriptions provided herein. For example, the precursordescribed above can be a cobalt, chromium or vanadium amidinates havingthe structure, [Co(AMD)_(m)]_(n), [Cr(AMD)_(m)]_(n) or [V(AMD)_(m)]_(n),where AMD is an amidinate and m=2 or 3 and n can range from 1 to 3.

EXAMPLES Example 1

The compound that served as a precursor for the manganese is calledbis(N,N′-diisopropylpropionamidinato)manganese(II), whose chemicalformula is shown below.

This compound was synthesized by the following method. All reactions andmanipulations were conducted under a pure dinitrogen atmosphere usingeither an inert atmosphere box or standard Schlenk techniques. Allglassware was stored in an oven at 150° C. for over 12 h before carryingreactions. Diethyl ether was purified using an Innovative Technologysolvent purification system, and was freshly used from the purificationwithout any storage. Butyllithium (1.6 M in hexanes),N,N′-diisopropylcarbodiimide, and manganese(II) chloride (anhydrousbeads) were purchased from Aldrich and used as received. Volumereduction and evaporation steps were performed in vacuo.

Bis(N,N′-diisopropylpropionamidinato)manganese(II). At −30° C., asolution of butyllithium (1.6 M in hexanes, 100 mL, 160 mmol) was addeddropwise to a well-stirred solution of N,N′-diisopropylcarbodiimide(20.2 g, 160 mmol) in 250 mL of diethyl ether. The pale-yellowishmixture was maintained at −30° C. for 4 h before being allowed to warmto ambient temperature. Manganese chloride (10.0 g, 79.5 mmol) was addedas a solid to the solution, and the reaction mixture was stirred untilall pinkish manganese chloride beads were reacted (ca. 48 h). Theresulting cloudy orange mixture was filtered through a pad of Celite ona glass frit to yield a clear orange-brown solution. All volatiles wereremoved, leaving a yellow-brown solid that was vacuum distilled at 120°C. at 20 mTorr into a condenser and receiving flask heated to over 60°C., the melting point of the product. The pale yellowish liquidcondensate solidified in the receiving flask as it cooled to roomtemperature, giving 27.4 g, 65 mmol, or 82% yield of pure product.Bis(N,N′-diisopropylpropionamidinato)manganese(II) is a pale yellowcrystalline solid that immediately turns black when exposed to air.

For the CVD experiments, the liquid manganese precursor was evaporatedat a temperature of 90° C. into a flow of highly purified nitrogen(concentrations of water and oxygen less than 10⁻⁹ of the N₂). The vaporpressure of the precursor is estimated to be around 0.1 mbar at thistemperature.

The silica substrates were either thermally oxidized silicon or silicadeposited by ALD or by plasma-enhanced CVD. The CVD was carried out in ahot-wall tube reactor (diameter 36 mm) within a tube furnace attemperatures between 200 and 400° C. and a total pressure of about 5Torr. The flow rate of N₂ carrier gas was 60 sccm. The amount ofmanganese deposited was measured by Rutherford backscatteringspectroscopy (RBS).

The MnSi_(x)O_(y) formation was evaluated by cross-sectionalhigh-resolution transmission electron microscopy (HRTEM). Theeffectiveness of the MnSi_(x)O_(y) as a barrier to diffusion of Cu wastested in four ways: optical appearance, sheet resistance, Cu silicideformation and capacitance-voltage (CV) analysis of capacitors. For Cudiffusion tests, layers of SiO₂ 8 nm thick were grown on HF-etchedsilicon wafers by ALD at 215° C., followed by CVD Mn at 350° C. for 10min, which deposited an amount of Mn metal equivalent to a Mn metal film2.3 nm thick, which reacted with the silica surface to form a thickerMnSi_(x)O_(y) layer. Control samples of SiO₂ omitted the CVD Mntreatment. Then Cu layers about 200 nm thick were deposited on top ofthe CVD MnSi_(x)O_(y) or SiO₂ layers Anneals in a pure nitrogenatmosphere were carried out at temperatures of 400, 450 and 500° C. forone hour. For CV analysis, CVD Mn was deposited on 300 nm thermal SiO₂.Cu pads (500 μm diameter circle) were formed by thermal evaporationthrough a shadow mask.

Thin Mn layers (equivalent to a Mn metal layer 2.3 nm thick) depositedon SiO₂ did not have significant electrical conductivity, presumablybecause the Mn reacts with the insulator to form MnSi_(x)O_(y) which hasa high resistivity. Thus, the deposition of metal Mn is not proven bythis result. To confirm that Mn metal was initially deposited, Mn wasdeposited on Cu 50 nm thick that had been evaporated onto SiO₂/Sisubstrates. The resulting structure was examined by cross-sectionalHRTEM. FIG. 11 shows that the CVD Mn metal diffused through the Cu layerand reacted with the SiO₂ to form an amorphous MnSi_(x)O_(y) layer about2-5 nm thick between the Cu and the SiO₂. The MnSi_(x)O_(y) layer isthicker near grain boundaries in the Cu, along which Mn diffusion isfaster. This result is clear evidence of Mn metal deposition.

These layers show strong adhesion after Mn deposition. No material wasremoved after a tape adhesion test. The adhesion of these layers wasmeasured more quantitatively by a 4-point bend test to be greater than 5J m⁻². This value is high enough to survive CMP and later mechanicalstresses in microelectronic devices. In control experiments, Cudeposited on SiO₂ without the subsequent Mn deposition was easily pulledoff by tape because of its poor adhesion.

The effectiveness of MnSi_(x)O_(y) as a copper barrier was evaluatedusing a sample structure PVD Cu(200 nm)/CVD Mn (2.3 nm)/ALD SiO₂ (8nm)/Si. A MnSi_(x)O_(y) layer was formed between the Cu and ALD SiO₂layers. The shiny Cu color and sheet resistances of these samples wereunchanged by anneals in nitrogen at 400 or 450° C. After a 500° C.anneal, the control sample without Mn turned black and its sheetresistance increased by a factor of 200 because of massive diffusion ofthe Cu through the thin ALD SiO₂ into the silicon. The CVD Mn sample, bycontrast, retained its shiny Cu color and showed only a slight increasein resistance even at 500° C.

To analyze for Cu diffusion, the remaining Cu layers were dissolved innitric acid, and then the manganese silicate and silica were removed bydilute HF. The etched surfaces were then analyzed by anenergy-dispersive X-ray spectrometer (EDX) and scanning electronmicrographs (SEM). FIG. 12 shows the SEM results after a 500° C. annealfor 1 hr. The few Cu-containing spots appear to be Cu silicidecrystallites oriented by the crystal directions of the silicon. Thecontrol sample shows that the majority of its surface is covered by Cusilicide. The control sample showed a large Cu signal in EDX analysisthat was stronger than the silicon signal, confirming that the thin ALDSiO₂ allowed diffusion of Cu. The CVD Mn-treated samples did not show Cuby large-area EDAX. A few small areas of the SEM image did show some Cuby EDAX, indicating some localized breakdown of the MnSi_(x)O_(y)barrier at 500° C. These spots might arise from dust or other defects inthe films, which were not processed in a clean-room environment.

An electrical test of barrier properties was carried out by patterningthe Cu into capacitor electrodes. CV curves for samples annealed at 450°C. for 1 hr are shown in FIG. 13. The large shift (−4.9 V) to negativevoltages in the control sample is caused by positive Cu ions diffusinginto the silica insulator. In contrast, the silica protected byMnSi_(x)O_(y) shows only a very small shift (−0.1 V). This electricaltest is more sensitive to diffusion of small amounts of Cu than theother tests. These CV curves also demonstrate that the capacitance ofthe SiO₂ is not changed significantly by the CVD Mn treatment.

Anneals of similar capacitors were also conducted under an appliedvoltage of 1 MV/cm at 250° C. Bias temperature stress (BTS) test is moresensitive method for Cu diffusion into SiO₂. The control sample lost thecapacitance behavior after just 2 minutes in the BTS condition (FIG. 14(a)), implying that a large amount of Cu diffused into the Si, so thatthe Si would not work as a semiconductor. However, the CVD Mn treatedsample had no significant change in its CV curve (FIG. 14( b)). Theresults of this BTS test confirm the good Cu barrier properties of theMnSi_(x)O_(y) layers.

MnSi_(x)O_(y) layers were also found to be good barriers to oxygen andwater, which can corrode copper layers. To test how well the metalsilicate layers protected copper, commercial low-k porous insulatorlayers from Applied Materials was coated with manganese as describedabove, followed by CVD copper. The top surface of the copper wasprotected with 20 nm of ALD silica by the process described in Science,volume 298, pages 402-406 (2002). The sample was cut into pieces toexpose the edges of the low-k insulator so that oxygen or water vaporcould diffuse into the low-k layer. After exposure to dry air at 300° C.for 24 hours, the sample maintained its shiny copper color. A controlsample without the CVD manganese treatment was corroded to dark copperoxide by the same exposure. This test shows that the manganese silicatelayer is a good barriers to oxygen. Similar tests in a humid atmosphere(85% humidity at 85° C. for 24 hours) showed that the manganese silicatelayer is a good barrier to water vapor.

The formation of the MnSi_(x)O_(y) layer increased the adhesion of theCu/SiO₂ interface, which failed the tape adhesion test prior to the CVDof Mn, but passed after the CVD of Mn. Adhesion strength was measured by4-point bend tests. The samples were prepared by CVD of Mn onto thermalSiO₂ on silicon wafers. Then CVD at 200° C. was used to form Cu by thereaction of vapors of copper N,N′-di-sec-butylacetamidinate and hydrogen(H₂). The adhesion energy was found to be 10.1±1 J m⁻². Generally, 5 Jm⁻² is considered to be a minimum threshold requirement for makingdurable interconnections.

A cross-sectional transmission electron microscope (TEM) was used tomake an image (FIG. 15) of a MnSi_(x)O_(y) layer in the surface of alow-k insulator. This image shows the MnSi_(x)O_(y) layer as a dark,featureless band, indicating that this layer is an amorphous glass.Conformality of the CVD Mn and CuON depositions in holes with aspectratios up to 40:1 was confirmed by cross-sectional SEM and TEM studies.

Example 2

Example 1 is repeated with manganese cyclopentadienyl tricarbonyl,MnCp(CO)₃, in place ofbis(bis(N,N′-diisopropyl-pentylamidinato)manganese(II). Similar resultsare obtained.

Example 3

Example 1 is repeated with chromium in place of manganese. Similarresults are obtained.

Example 4

Example 1 is repeated with vanadium in place of manganese. Similarresults are obtained.

Example 5

Improved adhesion between Mn-diffused Cu and a SiCN insulating film wasobtained. Quantitative 4-point bend tests of the adhesion energy betweenMn-diffused Cu and SiCN layers were carried out. 50 nm of copper wasevaporated onto SiCN layers (BLoK™, Applied Materials). The Cu showedvery poor adhesion, with adhesion energy less than 3 J m⁻². Next,similar Cu/SiCN layers were treated by CVD Mn at 350° C. for 10 minutes.This process increased the sheet resistance from 0.5 ohms/square to 1ohm per square because of the manganese impurity in the copper. Then thestructure was annealed for 1 hour at 400° C. in a nitrogen atmosphere.The sheet resistance then returned to slightly less than 0.5 ohms persquare because the manganese diffused to the surfaces or the interface.The out-diffusion of the manganese from the Cu film was confirmed bySIMS analysis. After the heat treatment, the adhesion energy wasremarkably increased to greater than 12 J m⁻², because manganesediffused to the interface, and made an interface or reaction layer. Theadhesion energy was greater than the 10.1±1 J m⁻² obtained in Example 1.

Example 6

Even greater adhesion between Mn-diffused Cu and Si₃N₄ layers wereobserved. 20 nm of Cu was deposited by CVD as in Example 1 on a siliconwafer that had been previously coated with Si₃N₄ by plasma-activatedCVD. Then 2.3 nm of Mn was deposited by the CVD process described inExample 1. Next another 20 nm of Cu was deposited by CVD, followed by 30nm of Si₃N₄ by plasma-activated CVD (PECVD). The adhesion of theselayers was so strong that they could not be separated during the 4-pointbend tests. Instead, the high-strength epoxy failed at debonding energydensities over 80 J m⁻². Accordingly, at least an 8-fold increase inadhesion was observed using Si₃N₄ layers rather than the silica layer ofExample 1.

Control samples made without the CVD Mn step failed at much lowerdebonding energy densities of about 7 J m⁻².

These results show that the bonding of Cu to a capping layer of Si₃N₄can be greatly strengthened by the addition of Mn to the Cu layer byCVD. The much stronger bonding of the Mn-doped Cu to the capping layercan suppress electromigration along the tops of the capped line. Thusthis capping process leads to a much greater lifetime of theinterconnect lines before they fail by electromigration. The interfacialbonding layer comprising Mn, Si and N bonds copper metal to Si₃N₄ morestrongly than an interfacial layer that includes oxygen.

Example 7

In addition, the Mn capping process is able to maintain the insulationbetween Cu lines. In order to demonstrate this effect, comb teststructures were prepared with long (˜4 cm) parallel Cu interconnectsseparated by SiO₂-based insulating lines 70 nm wide. The upper surfaceswere prepared by chemical-mechanical polishing to be substantially flat.The leakage current between the lines was less than 10⁻¹² amperes whenmeasured at 2 volts. After CVD of Mn as in Example 1 for 5 minutes andPECVD of 20 nm Si₃N₄, the leakage current remained at this low base-linelevel. The resistance along the length of the lines decreased slightlyfrom its initial value, possibly because of growth in the size of thecopper grains during the CVD processes.

Example 8

Substrates of several commercial insulating layers on silicon wereloaded into a CVD reactor, along with thin (20 nm) copper on oxidizedsilicon. These insulating samples included thermally-grown silicondioxide, plasma-deposited silicon dioxide and non-porous low-k siliconcarbide oxide (SiCOH) insulators with dielectric constants of 2.7 or2.5, as well as porous low-k SiCOH insulators with dielectric constantsof 2.4 or 2.2. Another substrate was patterned with areas of copperseparated by areas of non-porous SiCOH (k=2.5). All these samples hadreceived a chemical mechanical polish prior to the vapor treatments.After the substrates were loaded into the reactor they were flushed withpurified nitrogen while they were heated to 250° C. Then copper oxide onthe copper surfaces was reduced in purified hydrogen gas at 1 Torr for 1hour at 250° C. This treatment also removed adsorbed water from theinsulators. Next the reactor was cooled down to room temperature. Thentwo self-assembled monolayer (SAM) vapor pretreatments were applied, asfollows. The reactor was pumped down to the base pressure (about 20mTorr), and then filled with vapor (about 14 Torr) from aroom-temperature source of bis(N,N-dimethylamino)dimethylsilane,(CH₃)₂Si(N(CH₃)₂)₂ and then heated to 90° C. for ½ hour. Then thereactor was again pumped to base pressure, cooled to room temperatureand refilled with the vapor (about 75 Torr) of(N,N-dimethylamino)trimethylsilane, (CH₃)₃SiN(CH₃)₂ and heated to 90° C.for ½ hour. The samples were then heated to the manganese depositiontemperature of 300° C. The manganese precursor,bis(N,N′-diisopropylpentylamidinato)manganese(II), was evaporated fromthe liquid in a bubbler at a temperature of 90° C. into a 60 sccm flowof highly purified nitrogen (concentrations of water and oxygen lessthan 10⁻⁹ of the N₂). This vapor mixture was mixed with 60 sccm ofpurified hydrogen at a tee just prior to entering one end of a tubularreactor. The reactor tube has an inner diameter of 36 mm. A halfcylinder of aluminum supported the substrates inside the reactor. Thepressure in the reactor was maintained at 5 Torr by a pressure sensorcontrolling a butterfly valve between the reactor and the vacuum pump.After the temperature was stabilized, the CVD vapor mixture was passedthrough the reactor for 20 minutes. Then the reactor was cooled down toroom temperature and the samples removed for analysis.

Rutherford Backscattering Spectroscopy (RBS) was used to measure theamount of manganese deposited on the samples. The resulting data areshown in FIG. 16 for a copper substrate and for a low-k substrate(k=2.5). Analysis of these RBS data show that 6.6×10¹⁶ manganese atomsper square centimeter were deposited on and into the copper substrate,an amount that would form a layer 8 nm thick if it had the density ofbulk manganese metal. No manganese (detection limit <5×10¹³ atoms cm⁻²)could be detected by RBS on either sample of silicon dioxide or on anyof the low-k SiCOH insulators with k=2.4, 2.5 or 2.7. Thus this processhas selectivity >1000:1 in favor of deposition on Cu versus depositionon these insulators. The manganese content of the patterned samples wasalso measured by Energy-Dispersive Analysis by X-rays (EDAX) in aScanning Electron Microscope (SEM). 5.08 atomic % manganese was found inthe copper areas, whereas no manganese (<0.01%) was detected on theinsulating areas. According to the EDAX results, the selectivityis >500:1. X-ray Photoelectron Spectroscopy (XPS) also found manganeseon copper, but no manganese on non-porous insulators, showingselectivity >100:1, as shown by the bottom curve in FIG. 19. Because RBShas the greatest sensitivity of these analytical methods, we concludethat the selectivity exceeds 1000:1.

On the porous SiCOH insulator with k=2.2, a low level of Mn (1.2×10¹⁴atoms cm⁻²) was detected on the insulator, corresponding to aselectivity about 500:1.

The distribution of CVD manganese in a copper substrate, as determinedby XPS analysis, is shown in FIG. 17. The points are the experimentalvalues, and the line is a theoretical fit to the diffusion equation,assuming that the surface concentration of manganese remains constantduring the CVD process, and that the substrate is cooled quickly afterdeposition. The diffusion constant determined from this fit is 3×10⁻²¹m² s⁻¹, a value that is about 30 times larger than the value previouslyreported for diffusion of Mn into single-crystal Cu at 300° C.

Example 9

Samples of the porous SiCOH insulators (k=2.2 or 2.4) were firstsubjected to pore-sealing by ALD SiO₂, as described in the patentapplication US2008/0032064, which is incorporated by reference herein inits entirety. Then they were treated with CVD manganese as described inExample 8. Analyses by RBS, EDAX and XPS showed that no manganesedeposited on the sealed surfaces of the insulators.

Example 10

Additional tests were carried out to see how much manganese is requiredto increase the adhesion between copper and insulators onto which it isdeposited. Insulating substrates of silicon dioxide, silicon nitride andsilicon carbon nitride were used. First CVD was used to form a copperlayer on the insulators as in Example 1, then CVD of manganese wascarried out as in Example 1, and then a second CVD copper layer wasdeposited. These samples were taken through an air break into a chamberin which they received about 0.1 μm of sputtered aluminum, and then theywere attached by high-strength epoxy to a piece of a second siliconwafer. Adhesion testing by the 4-point probe method gave the resultsshown in FIG. 18, in which the debonding energy is plotted against theratio of manganese to silicon remaining on the fracture surface of theinsulator, as determined by XPS. These results show that increasingamounts of manganese at the interface between the copper and aninsulator greatly increases the adhesion strength between thesematerials.

Example 11

Additional tests were carried out to see how manganese strengthens theinterface between a previously-deposited copper layer and siliconnitride subsequently deposited on top of the copper. First, titanium wassputtered onto a substrate of thermally oxidized silicon, followed by asputtered copper layer. Following an air break, the oxidized coppersurface was reduced by heating in purified hydrogen gas at 1 Torr for 1hour at 250° C. Then CVD manganese was applied as described in Example8. After another air break, the sample was treated by an ammonia plasmaand then a plasma-CVD silicon nitride layer about 20 nm thick wasdeposited prior to sputtering 0.1 μm of aluminum. The fracture occurredat the interface between the silicon nitride and the copper onto whichit was deposited. The fracture energies at this capping interface arealso plotted in FIG. 18, which shows that it is bonded even morestrongly than the copper-manganese deposited on top of substrates ofsilicon nitride as described in Example 10.

Comparative Example 1

A control experiment was carried out for comparison with Example 8. Thesteps in Example 8 were repeated, except that the reactions withbis(N,N-dimethylamino)dimethylsilane, (CH₃)₂Si(N(CH₃)₂)₂ and(N,N-dimethylamino)trimethylsilane, (CH₃)₃SiN(CH₃)₂ were omitted. About3×10¹⁵ manganese atoms per square centimeter were found on the surfaceof the insulator by RBS analysis. Although XPS does not count the atomsas quantitatively as RBS does, this amount of manganese was readilyobserved by XPS, as shown in the top curve in FIG. 19.

Comparative Example 2

A control experiment was carried out for comparison with Example 8. Thesteps in Example 8 were repeated, except that the reaction withbis(N,N-dimethylamino)dimethylsilane, (CH₃)₂Si(N(CH₃)₂)₂ was omitted andonly the reaction with (N,N-dimethylamino)trimethylsilane,(CH₃)₃SiN(CH₃)₂, was carried out. Manganese was detected by XPS on thesurface of the insulators, so complete selectivity was not obtained, asshown in the second curve from the top in FIG. 19.

Comparative Example 3

A control experiment was carried out for comparison with Example 8. Thesteps in Example 8 were repeated, except that the reaction with(N,N-dimethylamino)trimethylsilane, (CH₃)₃SiN(CH₃)₂ was omitted and onlythe reaction with bis(N,N-dimethylamino)dimethylsilane,(CH₃)₂Si(N(CH₃)₂)₂, was carried out. Manganese was detected by XPS onthe surface of the insulators, so complete selectivity was not obtained,as shown in the third curve from the top in FIG. 19.

The conclusion from comparative examples 1, 2 and 3 is thatpre-treatments with both bis(N,N-dimethylamino)dimethylsilane,(CH₃)₂Si(N(CH₃)₂)₂, and (N,N-dimethylamino)trimethylsilane,(CH₃)₃SiN(CH₃)₂ aids in minimizing deposition of manganese on insulatorsduring the stabilization of copper surfaces by CVD manganese.

Comparative Example 4

A control experiment was carried out for comparison with Example 8. Thesteps in Example 8 were repeated, except that the flow of hydrogen, H₂,was replaced by a flow of nitrogen, N₂. XPS analysis showed the presenceof manganese on the surfaces of insulators. The conclusion fromcomparative example 4 is that the presence of hydrogen during CVD aidsin minimizing deposition of manganese on insulators during thestabilization of copper surfaces by CVD manganese.

Example 12

Cobalt metal was deposited selectively by CVD on copper surfaces, whilelittle or no cobalt was deposited on suitably pretreated insulatorsurfaces. Substrates of copper and silica were first prepared by heatingin purified hydrogen gas at 1 Torr for 1 hour at 250° C., and thenexposed to the silane vapors as described in Example 8.Bis(N-tert-butyl-N′-ethylpropionamidinato)cobalt(II) was prepared asdescribed in the paper “Synthesis and characterization of volatileliquid cobalt amidinates”, published in Dalton Transactions of the RoyalSociety of Chemistry, pages 2592-2597 in 2008, which is incorporated byreference herein in its entirety. This liquid cobalt precursor wasplaced in a bubbler at 85° C., at which temperature it has a vaporpressure about 0.26 Torr. Its vapor was delivered to the CVD reactor bypassing 60 sccm of high purity N₂ gas through the bubbler. Theco-reactant gas, H₂, with a flow rate of 60 sccm, was mixed with theprecursor vapor stream just prior to entering the CVD reactor. Thesubstrates were held at a temperature of 200° C. Deposition for 20minutes was sufficient to cover the copper surface completely withcobalt. The evidence for this coverage is that XPS showed only signalsfor cobalt, with no signals characteristic of copper. On the silicasurface, no XPS signals for cobalt were detected, while the RBS analysisshowed less than 10¹⁴ cobalt atoms per square centimeter.

Example 13

Plasma-enhanced silica layers on silicon were used as substrates formanganese deposition under conditions described in Example 1 to formMnSi_(x)O_(y) layers. Then CVD manganese nitride was deposited byreacting the same manganese precursor with ammonia at a partial pressureof 2 Torr and hydrogen at a partial pressure of 1 Torr, and a substratetemperature of 130° C. for 5 minutes, resulting in a coating withcomposition Mn₄N about 2.5 nm thick. The root-mean-square surfaceroughness was measured by atomic force microscopy to be 0.3 nm, which isbarely larger than that of the substrate, 0.2 nm. This result shows thatthe manganese nitride remains smooth and does not agglomerate at thislow deposition temperature.

Example 14

Manganese nitride was deposited as in Example 13. The manganese nitridelayer was then reduced by hydrogen plasma at a substrate temperaturejust above room temperature (heated to about 50° C. by recombination ofhydrogen atoms on the surface) to produce a smooth, non-agglomeratedlayer of manganese metal.

Example 15

As another example of CVD of manganese nitride, the manganese precursorwas evaporated from the liquid in a bubbler at a temperature of 90° C.into a 60 sccm flow of highly purified nitrogen (concentrations of waterand oxygen less than 10⁻⁹ of N₂). This vapor mixture was mixed with 60sccm of highly purified nitrogen and 60 sccm of purified ammonia (NH₃)at a tee just before entering one end of a tubular reactor. The reactortube had an inner diameter of 36 mm. A half-cylinder of aluminumsupported the substrates inside the isothermal reactor. The reactortemperature was controlled at 130° C. and the total pressure in thereactor was maintained at 5 Torr by a pressure sensor controlling abutterfly valve between the reactor and the vacuum pump. Under theseconditions, about 2.5 nm of manganese nitride film was deposited in 5minutes.

Substrates having holes with aspect ratio (ratio of length to diameter)of 52:1 were coated in this way with MnN_(x), x˜0.25. FIG. 20 shows aSEM of a cross section through some of these holes. The bright lineoutlining the holes comes from the MnN_(x) film, showing that thematerial was deposited uniformly and conformally over the insidesurfaces of these holes. X-ray diffraction showed that the material hasthe cubic structure known for Mn₄N. Atomic force microscopy (AFM) showedthat Mn₄N films are fairly smooth, with a root-mean-square roughnessequal to 7% of their thickness.

Example 16

Mn₄N was deposited as in Example 15. The Mn₄N film was kept in thereactor in a flow of pure nitrogen while it was cooled to about 50° C.,in order to protect its surface from oxidation. Ethyl iodide vapor(CH₃CH₂I, boiling point 72° C.) was then used as an iodine source toadsorb iodine atoms onto the fresh surface of the manganese nitridefilm. The ethyl iodide was contained in a bubbler at room temperatureand its vapor was fed directly into the reactor at a partial pressure of0.05 Torr for 30 seconds along with a nitrogen carrier gas at a flowrate of 100 sccm and a total pressure of 0.5 Torr. CVD copper was thendeposited in the same reactor using copper precursor evaporated from theliquid in a bubbler at a temperature of 130° C. into a 40 sccm flow ofhighly purified nitrogen. Hydrogen (40 sccm) was mixed with the copperprecursor vapor just before entering the reactor held at a substratetemperature of 180° C. and a total pressure of 5 Torr. Under theseconditions, about 65 nm of copper was deposited in 40 minutes.

FIG. 21 shows that this process completely filled trenches less than 30nm wide and over 150 nm deep with copper, with an aspect ratio over 5:1.No seams or voids were seen along the centerline of the copper,suggesting that iodine pre-adsorbed on the Mn₄N was released from theMn₄N and then catalyzed the bottom-up filling of these trenches as asurfactant floating on the growing surface of the copper. FIG. 22 showsthat after the deposition iodine is found only on the top surface of thecopper by X-ray photoelectron spectroscopy (XPS). Signals of iodinedisappear together with signals of oxygen and carbon from surfacecontamination as the film is sputtered from the top, and no impuritiesare detectable in the bulk of the copper film. These XPS data prove thatthe iodine was successfully released from the Mn₄N surface, and floatedas a catalytic surfactant on the growing copper surface. Even narrowertrenches, with widths as low as 17 nm, depths over 150 nm and aspectratios of 9:1, were also filled successfully with Cu by this process, asshown by the SEM in FIG. 23. Conventionally, it had been believed thatcatalytic CVD of copper could not provide void-free filling of trenchesif their aspect ratio was over 5:1. However, contrary to conventionalwisdom, substantially void-free filling of trenches was achieved withCVD of copper catalyzed by iodine released from the surface of theMnN_(x). Wider trenches were partially filled with copper by the samedeposition conditions, as shown in FIG. 24. The fact that the coppergrew faster from the bottom than from the sides of the trench shows thatthe iodine catalyst was released from the surface of the MnN_(x) layer.

Another surprising observation from the micrographs in FIG. 21 is thatlarge copper grains completely cross the width of the trenches, evenwithout any post-deposition annealing. This “bamboo structure” is highlydesirable, because it extends the lifetimes of copper lines before theyfail by electromigration. Another factor that extends theelectromigration lifetime is if the adhesion of the copper to thesurrounding material is strong. Therefore we tested the adhesion ofplanar copper films grown on Mn₄N according to the process described inExample 16. Following the deposition, the structures were annealed at350° C. for one hour in a pure nitrogen gas ambient. 4-point bend testson these samples showed debonding energies greater than 6.5 Joules persquare meter, which is a value high enough to survive furtherfabrication by chemical-mechanical polishing.

The effectiveness of manganese nitride as a barrier to diffusion ofcopper was tested by looking for its reaction with silicon to formcopper silicide. For this copper diffusion test, layers of SiO₂ 9 nmthick were grown on HF-etched silicon wafers by atomic layer deposition(ALD) at 250° C., followed by CVD manganese nitride at 130° C. for 5min, which formed 2.5 nm of film, and a post-deposition anneal at 350°C. for 1 hour under nitrogen ambient. Control samples of SiO₂ omittedthe CVD manganese nitride treatment. Copper layers about 200 nm thickwere then deposited on top of the manganese nitride or SiO₂ layers. Thesamples were then annealed in a pure nitrogen atmosphere at 500° C. for1 hour. To see if copper had diffused into the silicon substrate, the Culayers were dissolved in nitric acid, and the manganese nitride andsilica were removed by dilute HF. The etched surfaces were then analyzedby an energy-dispersive X-ray spectrometer (EDX) and SEM with theresults shown in FIG. 25. The reference sample shows that the majorityof its surface is covered by copper silicide crystallites, indicatingcopper has diffused through the thin silica layer. The manganesenitride-treated sample does not show any Cu by large-area EDX, showingthat MnN_(x) or its reaction product with SiO₂ forms an effectivebarrier against diffusion of copper.

Comparative Example 5

Example 16 was repeated, except that the CVD of MnN_(x) was omitted.Thus ethyl iodide vapor was exposed to the bare SiO₂ surface, ratherthan to MnN_(x). Much less copper was deposited than in Example 16, andwhat copper was present was in the form of agglomerated grains, ratherthan as a conformal film or a filling of narrow trenches. Thiscomparative result shows that SiO₂ is unable to chemisorb iodine andthen release it to serve as a catalytic surfactant, as compared to theMnN_(x) as shown in Example 16.

Example 17

Example 16 was repeated, except that the first copper layer was grownonly for 5 minutes. Then an additional step of iodine adsorption wasapplied to the fresh copper surface. Then additional CVD of Cu wascarried out for 40 minutes. Similar results were found, with thedifference that the total amount of copper deposited was 50% larger thanin Example 16, presumably because of the additional amount of iodinecatalyst that was supplied.

Example 18

Manganese nitride was first deposited at 130° C. for 5 minutes to form2.5 nm of film. Ethyl iodide was then introduced into the chamber at 50°C. for 30 seconds at a pressure of 0.05 Torr. Copper was then depositedat 180° C. for 5 minutes to form a continuous layer, and ethyl iodidevapors were again exposed to the Cu surface at 50° C. for 30 seconds.Manganese and copper precursors were then alternatively carried into thechamber by 50 sccm of nitrogen and mixed with 50 sccm of hydrogen at asubstrate temperature of 180° C. and a total pressure of 5 Torr. In onecycle, the manganese precursors were supplied for 3 minutes and thecopper precursors were supplied for 5 minutes. This cycle was repeateduntil the trenches were completely filled with a copper-manganesenanolaminate. The Mn/Cu ratio was quantified by X-ray fluorescence (XRF)and was found to be approximately 0.5 atomic percent manganese. TheCu—Mn nanolaminate completely filled narrow trenches, as shown by theSEM in FIG. 26. The iodine catalyst was found on the top of thenanolaminate surface by XPS, as shown in FIG. 27.

After annealing, samples prepared according to Example 18 show strongeradhesion to insulator surfaces such as SiO₂, Si₃N₄ and low-k insulators.When the ratio of manganese to silicon exceeds about 0.5 at theinterface between the Cu—Mn and the insulator, the debonding energybecomes larger than about 15 Joules per square meter. Such stronginterfaces cannot be broken during the 4-point bend test. This verystrong adhesion is expected to greatly increase the lifetime of copperinterconnects before they fail by electromigration. The amount ofmanganese in the copper to achieve this interfacial concentration willdepend on the size and shape of the copper interconnect. Concentrationof manganese in the copper in the range from 0.1% to 4% or morepreferably between 0.2% and 2% may be sufficient to obtain the strongadhesion to insulator surfaces.

Example 19

Example 18 was repeated up through the second iodine exposure. Then theMn precursor vapors were carried by 60 sccm of nitrogen andsimultaneously the Cu precursor vapors were carried by 40 sccm ofnitrogen. These precursor vapor flows were mixed together with 100 sccmof hydrogen at a temperature of 120° C. and a pressure of 5 Torr. Thisgas mixture flowed into the deposition zone heated to 180° C. for 45minutes. The trenches were completely filled with a copper-manganesealloy, as shown in FIG. 28, and the tops of the trenches were covered byabout 180 nm of Cu—Mn alloy. The Mn/Cu ratio in the alloy was quantifiedby XRF and was found to be approximately 0.4 atomic percent manganeseand 99.6 copper. The iodine catalyst was found on the top surface of thecopper-manganese alloy by XPS, as shown in FIG. 29.

It should be noted that the proposed explanation regarding the existenceof manganese nitride providing sufficient balance of chemisorption andsubsequent release of the iodine fails to explain the successful resultsof Examples 18 and 19, in which most of the manganese has no nearbynitrogen. The manganese that is mixed with the copper layer is not closeto any nitrogen, and thus would be expected to bind strongly to theiodine and make it unavailable as catalytically active iodine on thecopper surface. Nevertheless, Applicants have verified that the iodineinitially adsorbed on MnN_(x) or on Cu “floats” to the surface duringsubsequent CVD of the Cu—Mn alloy, despite the presence of Mn within thealloy. Despite the fact that Mn is known to form stronger bonds toiodine than Cu, and despite the fact that there is no nearby nitrogen toweaken the interaction between iodine and Mn, Applicants surprisinglydemonstrate the successful catalytic growth of copper usingiodine-containing precursors even in these examples.

Example 20

The Mn precursor is dissolved at a concentration of 0.5 M in an inertsolvent, 1-methylnaphthalene, the solution is vaporized by a directliquid injection system, mixed with ammonia gas, and flowed into areactor to form a MnN_(x) layer. The surface of the MnN_(x) is thenexposed to ethyl iodide as in Example 16. The Cu precursor is dissolvedat a concentration of 1 M in an inert solvent, 1-methylnaphthalene, thesolution is vaporized by a direct liquid injection system, mixed withhydrogen gas, and flowed into the reactor to form a thin Cu layer. Thesurface of the Cu is then exposed to ethyl iodide as in Example 18. Thenseparately measured and controlled flows of Cu and Mn precursor solutionare simultaneously vaporized in a DLI system, and the resulting mixedvapors, along with the solvent vapor and hydrogen gas, are introducedinto the CVD reactor. Results similar to Example 19 are obtained.

Example 21

Example 20 is repeated, except that the Mn and Cu precursors aredissolved together in an inert solvent, 1-methylnaphthalene, and thesolution is vaporized in a direct liquid injection system. The mixedprecursor vapors, along with the solvent vapor and hydrogen gas, arethen introduced into the CVD reactor during the last deposition step,co-deposition of a Cu—Mn alloy. Results similar to Examples 19 and 20are obtained. The 1-methylnaphthalene used in Examples 20 and 21 may bereplaced by other inert solvents with high boiling points, such asdiethyl benzene, tetrahydronaphthalene and pristane.

Example 22

Example 16 was repeated using substrates of various plastics that arestable up to the deposition temperature of 180° C. Prior to thedeposition, the surfaces of the plastics were cleaned and oxidized byexposure to light from a mercury lamp with a quartz envelope in ambientair for 5 minutes. After deposition, the surfaces of the plastics werecovered by electrically conductive copper films with sheet resistancearound 0.5 ohms per square. The smooth surface of a polyimide plasticsheet remained smooth, as shown in FIG. 30. The rough surface of afiberglass-reinforced circuit board was covered conformally, as shown inFIG. 31. The copper adhered strongly to the plastics, and could not beremoved by a tape test.

Example 23

CVD in accordance with one or more of the previous examples can be usedto form a thin layer comprising Mn and Cu with a small amount of I onthe surface. The thin layer comprising Mn, Cu, and I can serve as a seedlayer for electroplating a thicker layer of Cu. In a substrate with bothnarrow and wide trenches, the CVD steps may fill the narrow trenches,while conformally coating the wider trenches. Subsequent electroplatingcan then fill the wider trenches economically.

A small amount of iodine (much less than a monolayer) is attached to thecopper surface at the beginning of the electroplating step of Example23. There is a possibility that this iodine could dissolve in the copperplating bath and contaminate it. Alternatively, the iodine might remainunder the plated copper and cause corrosion or reliability problemslater. Therefore it could be advantageous to remove the iodine from thecopper surface prior to plating. The following two examples presentnovel methods for removal of the residual iodine from the surface ofcopper or copper-manganese alloys.

Example 24

A CVD MnN_(x)—CVD Cu—Mn sample was prepared as in Example 19. The samplewas then placed into a solution of 30% hydrogen peroxide-70% water for 1minute at room temperature. It was then rinsed in isopropanol and dried.Examination of the surface by XPS showed that no iodine remained on thesurface. Other oxidizing agents, such as sodium hypochlorite or sodiumhypobromite, may be substituted for the hydrogen peroxide, in order toremove the iodine from the copper surface.

Example 25

A CVD MnN_(x)—CVD Cu—Mn sample was prepared as in Example 19. The samplewas then placed in a reactive ion-etch system. It was first treated byan oxygen plasma with 150 watt microwave power and 50 watt RF power at10 mTorr pressure for 30 seconds at room temperature. It was thentreated by a hydrogen plasma with 150 watt microwave power and 50 wattRF power at 10 mTorr pressure for 3 minutes at room temperature.Examination of the surface by XPS showed that no iodine remained on thesurface.

In the case that only narrow trenches are to be filled with copper, itmay be desirable to prevent growth of copper on the flat upper surfaceof the substrates, in order to minimize the amount of copper that mayneed to be removed subsequently by CMP. This selective process isoutlined in Example 26.

Example 26

Example 19 is repeated, except that after the second iodine exposure,the plasma treatment of Example 25 is applied to remove the iodinecatalyst from the upper flat surface of the substrate. The plasmaprocess is limited to a time short enough so that iodine is not removedfrom the sides and bottoms of the narrow trenches. Then the remainingsuperfill of the trenches is completed by iodine-catalyzed CVD ofcopper-manganese alloy. Only a small amount of copper-manganese alloyforms on the top surface, along with some bumps over the trenches. Thissmall overburden of copper-manganese alloy is readily removed by a shortCMP process.

If the iodine catalyst is removed from the upper part of the sidewallsof the trenches, then the bottom-up growth can proceed further beforecopper growing from the upper parts of the sidewalls of the trench meetand prevent further growth of copper below the point of closure. Thustrenches and vias with higher aspect ratios can be filled without voidsor seams. This selective process for filling narrower and deepertrenches is illustrated in Example 27.

Example 27

Example 26 is repeated, except that the oxygen plasma and the hydrogenplasma are applied for a longer time, so that the iodine is removed fromthe upper sidewalls of very narrow trenches, as well as from the flattop surfaces between the trenches. Trenches with aspect ratios higherthan 10:1 are filled without voids or seams.

If the iodine catalyst is removed from most of the sidewalls of verynarrow trenches, and in addition the nucleation rate of copper issuppressed on the upper parts of the sidewalls and the tops of thetrenches, then extremely narrow trenches can be filled without voids orseams. One approach to suppressing the nucleation of copper is to reactthe copper (and manganese, if present) on the upper sidewalls with areactant vapor, such as an alkanethiol. Once an alkanethiol ischemisorbed on the surface of the copper, applicants have found thatfurther growth of copper by CVD is greatly retarded or even eliminated.Use of iodine removal followed by inactivation of the copper surface onthe sidewalls is illustrated by Example 28.

Example 28

Example 27 is repeated using substrates having with very narrow trencheswith aspect ratio greater than 20:1. Following the plasma-activatedremoval of the iodine from most of the trench walls, the surface isexposed briefly to a small amount of vapor of octanethiol. Subsequently,CVD copper-manganese is continued with the benefit of iodine catalystfrom the bottom and lower sidewalls of the trenches. The trenches arefilled with copper-manganese alloy without any voids or seams.

Those skilled in the art may make various modifications and additionswithout departing from the spirit and scope of the present contributionto the art.

We claim:
 1. A process for forming an integrated circuit interconnectstructure, said process comprising: a) providing a partially-completedinterconnect structure having one or more vias and trenches, said viasand trenches comprising sidewalls defined by one or more electricallyinsulating materials and electrically conductive copper-containingbottom regions; b) depositing a layer comprising a nitride of a metalselected from the group consisting of manganese, chromium and vanadiumon the partially-completed interconnect structure; c) depositing copperwithin said one or more vias and trenches.
 2. The process of claim 1,further comprising removing nitrogen from said layer comprising metalnitride prior to said depositing copper within said one or more vias andtrenches.
 3. The process as in claim 2 wherein said removing nitrogen isaccomplished by contact of the structure with a hydrogen-containingplasma.
 4. The process as in claim 1 wherein said depositing coppercomprises electroplating or electroless plating from a liquid solution.5. The process as in claim 1 wherein said depositing copper comprisesdeposition from the vapor phase by CVD or ALD.
 6. The process as inclaim 1, wherein said layer comprising a nitride of a metal comprisesmanganese nitride.